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Takuhei Nose - One of the best experts on this subject based on the ideXlab platform.
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multimolecular micelle formation of poly methyl methacrylate graft polystyrene in acetonitrile acetoacetic acid ethyl ether
Macromolecules, 1997Co-Authors: Atsushi Kikuchi, Takuhei NoseAbstract:Multimolecular-micelle formation is investigated by means of light scattering for poly(methyl methacrylate)-graft-polystyrene with low Grafted-Chain density in a dilute solution of mixed selective solvent of acetonitrile and acetoacetic acid ethyl ether. Molecular weights of the poly(methyl methacrylate) (PMMA) backbone and the polystyrene (PS) branch are about 5.6 × 106 and 9.2 × 103, respectively, and the Grafted-Chain density is 13 wt % PS. The mixed solvent is a marginally-good solvent to PMMA and is a nonsolvent to PS. Time evolutions of apparent molecular weight Mapp, radius of gyration Rgapp, and hydrodynamic radius Rhapp are measured in the course of micellization after quenching from the unimer region to the micelle region. Observed Mapp dependences of Rgapp, Rhapp, and Rgapp/Rhapp demonstrate the following features of multimolecular-micelle formation. Unimolecular micelles, which are made of a few linearly-connected flowers with small cores of associated PS branches and petals of PMMA backbone, ...
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unimolecular micelle formation of poly methyl methacrylate graft polystyrene in mixed selective solvents of acetonitrile acetoacetic acid ethyl ether
Macromolecules, 1996Co-Authors: Atsushi Kikuchi, Takuhei NoseAbstract:Unimolecular micelle formation is investigated by means of light scattering for poly(methyl methacrylate)-graft-polystyrene copolymers with low Grafted Chain densities in dilute solution of mixed selective solvents. Molecular weights of poly(methyl methacrylate) (PMMA) backbone and polystyrene (PS) branch are about 6 × 106 and 9 × 103 g mol-1, respectively, and the Grafted Chain density ranges from 6 to 17 wt % in terms of PS composition. The mixed solvents are marginally good solvents for PMMA and are nonsolvents for PS. From the results of static and dynamic light scattering measurements as a function of temperature and solvent composition, it is demonstrated that, at higher branch densities and lower temperatures, the rod like unimolecular micelles are formed, made of a few linearly connected flowers with small cores of associated PS branches and petals of PMMA backbone Chain. The number of petals per flower increases with increasing branch density and decreasing solubility of solvents for PMMA. On the...
Atsushi Kikuchi - One of the best experts on this subject based on the ideXlab platform.
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multimolecular micelle formation of poly methyl methacrylate graft polystyrene in acetonitrile acetoacetic acid ethyl ether
Macromolecules, 1997Co-Authors: Atsushi Kikuchi, Takuhei NoseAbstract:Multimolecular-micelle formation is investigated by means of light scattering for poly(methyl methacrylate)-graft-polystyrene with low Grafted-Chain density in a dilute solution of mixed selective solvent of acetonitrile and acetoacetic acid ethyl ether. Molecular weights of the poly(methyl methacrylate) (PMMA) backbone and the polystyrene (PS) branch are about 5.6 × 106 and 9.2 × 103, respectively, and the Grafted-Chain density is 13 wt % PS. The mixed solvent is a marginally-good solvent to PMMA and is a nonsolvent to PS. Time evolutions of apparent molecular weight Mapp, radius of gyration Rgapp, and hydrodynamic radius Rhapp are measured in the course of micellization after quenching from the unimer region to the micelle region. Observed Mapp dependences of Rgapp, Rhapp, and Rgapp/Rhapp demonstrate the following features of multimolecular-micelle formation. Unimolecular micelles, which are made of a few linearly-connected flowers with small cores of associated PS branches and petals of PMMA backbone, ...
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unimolecular micelle formation of poly methyl methacrylate graft polystyrene in mixed selective solvents of acetonitrile acetoacetic acid ethyl ether
Macromolecules, 1996Co-Authors: Atsushi Kikuchi, Takuhei NoseAbstract:Unimolecular micelle formation is investigated by means of light scattering for poly(methyl methacrylate)-graft-polystyrene copolymers with low Grafted Chain densities in dilute solution of mixed selective solvents. Molecular weights of poly(methyl methacrylate) (PMMA) backbone and polystyrene (PS) branch are about 6 × 106 and 9 × 103 g mol-1, respectively, and the Grafted Chain density ranges from 6 to 17 wt % in terms of PS composition. The mixed solvents are marginally good solvents for PMMA and are nonsolvents for PS. From the results of static and dynamic light scattering measurements as a function of temperature and solvent composition, it is demonstrated that, at higher branch densities and lower temperatures, the rod like unimolecular micelles are formed, made of a few linearly connected flowers with small cores of associated PS branches and petals of PMMA backbone Chain. The number of petals per flower increases with increasing branch density and decreasing solubility of solvents for PMMA. On the...
Jacques Jestin - One of the best experts on this subject based on the ideXlab platform.
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synthesis of polyisoprene polybutadiene and styrene butadiene rubber Grafted silica nanoparticles by nitroxide mediated polymerization
Polymer, 2020Co-Authors: Sanat K. Kumar, Didier Gigmes, Marine Bonnevide, Trang N T Phan, Nicolas Malicki, Marc Couty, Jacques JestinAbstract:Abstract We present a new application of nitroxide mediated polymerization (NMP) for grafting of various elastomers onto the surfaces of silica nanoparticles (NPs) while ensuring colloidal stability and thus avoiding particle aggregation. While NMP has been used to graft Chains from NP surfaces, our novel contributions are thus two-fold. We show for the first time that this methodology, initially demonstrated for styrene polymerization, can be extended to a variety of other relevant polymer chemistries, i.e., to isoprene, butadiene and styrene-butadiene rubber. We optimize the synthesis conditions for the different monomers under critical pressure conditions and characterize the Grafted Chains in solution by a combination of small angle x-ray and neutron scattering (with deuterated solvent labelling) to quantitatively describe the Grafted Chain composition. Second, crucially, we characterized the colloidal stability of the particles during the different steps of the grafting process. We have found that particle aggregation can (and does) occur at a variety of points during synthesis, and hence we have performed a detailed refined characterization of NP agglomeration and then found methods to mitigate it at each stage. These steps ensure that we can begin the preparation of composite materials from a well-defined starting point.
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accelerated local dynamics in matrix free polymer Grafted nanoparticles
Physical Review Letters, 2019Co-Authors: Mayank Jhalaria, Jacques Jestin, Michaela Zamponi, Eileen Buenning, Y Huang, Madhusudan Tyagi, Reiner Zorn, Victoria Garciasakai, Brian C Benicewicz, Sanat K. KumarAbstract:The tracer diffusion coefficient of six different permanent gases in polymer-Grafted nanoparticle (GNP) membranes, i.e., neat GNP constructs with no solvent, show a maximum as a function of the Grafted Chain length at fixed grafting density. This trend is reproduced for two different NP sizes and three different polymer chemistries. We postulate that nonmonotonic changes in local, segmental friction as a function of graft Chain length (at fixed grafting density) must underpin these effects, and use quasielastic neutron scattering to probe the self-motions of polymer Chains at the relevant segmental scale (i.e., sampling local friction or viscosity). These data, when interpreted with a jump diffusion model, show that, in addition to the speeding-up in local Chain dynamics, the elementary distance over which segments hop is strongly dependent on graft Chain length. We therefore conclude that transport modifications in these GNP layers, which are underpinned by a structural transition from a concentrated brush to semidilute polymer brush, are a consequence of both spatial and temporal changes, both of which are likely driven by the lower polymer densities of the GNPs relative to the neat polymer.
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polymer Grafted magnetic nanoparticles in nanocomposites curvature effects conformation of Grafted Chain and bimodal nanotriggering of filler organization by combination of Chain grafting and magnetic field
Macromolecules, 2012Co-Authors: Annesophie Robbes, Florent Dalmas, Didier Gigmes, Ralf Schweins, Fabrice Cousin, Florian Meneau, Jacques JestinAbstract:We present the synthesis and structural characterization of new nanocomposites made of linear tetramers of spherical magnetic nanoparticles of maghemite (γ-Fe2O3), Grafted by tethered polystyrene (PS) Chains with an intermediate grafting density (∼0.15 Chains/nm2), dispersed in a PS matrix. First, we studied by combination of SAXS and TEM the dispersion state of the Grafted objects within the matrix for various ratio R of the mass of the Grafted Chains N to the mass of free Chains P ranging from R = N/P = 0.09 to R = 2.83. For R 1, the objects are also well dispersed although there are some remaining aggregates, arising probably from the fact that we have used matrix’ Chains below the entanglement mass to r...
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controlled grafting of polystyrene on silica nanoparticles using nmp a new route without free initiator to tune the Grafted Chain length
Polymer Chemistry, 2011Co-Authors: Chloe Chevigny, Didier Gigmes, Denis Bertin, Jacques Jestin, Ralf Schweins, Francois BoueAbstract:We synthesized well-defined polystyrene-Grafted silica nanoparticles by adapting our previous synthesis process without using free initiator. We were able to obtain a more versatile system in which we can tune the masses of the Grafted Chains while controlling the polymerization, the colloidal stability and avoid the formation of free polymer Chains. The final Grafted objects were characterized in a refined way using SANS and the contrast matching method.
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polymer Grafted nanoparticles nanocomposites dispersion Grafted Chain conformation and rheological behavior
Macromolecules, 2011Co-Authors: Chloe Chevigny, Florent Dalmas, Emanuela Di Cola, Didier Gigmes, Denis Bertin, Francois Boue, Jacques JestinAbstract:We investigate the dispersion mechanisms of nanocomposites made of well-defined polymer (polystyrene, PS) Grafted-nanoparticles (silica) mixed with free Chains of the same polymer using a combination of scattering (SAXS/USAXS) and imaging (TEM) techniques. We show that the relevant parameter of the dispersion, the Grafted/free Chains mass ratio R tuned with specific synthesis process, enables to manage the arrangement of the Grafted nanoparticles inside the matrix either as large and compact aggregates (R 0.24). From the analysis of the interparticles structure factor, we can extract the thickness of the spherical corona of Grafted brushes and correlate it with the dispersion: aggregation of the particles is associated with a significant collapse of the Grafted Chains, in agreement with the theoretical models describing the free energy as a combination of a mixing entropy term between the free and the Grafted Chains and an elastic term of deformation ...
Pinar Akcora - One of the best experts on this subject based on the ideXlab platform.
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understanding the role of Grafted polystyrene Chain conformation in assembly of magnetic nanoparticles
Physical Review E, 2014Co-Authors: Yang Jiao, Pinar AkcoraAbstract:Polystyrene-Grafted iron oxide nanoparticles have been shown to phase separate into ordered morphologies of strings, well-dispersed particles, and spherical aggregates at low graft densities in polymer matrices. In this work, small-angle neutron scattering experiments are performed to reveal the role of Grafted Chain conformation on nanoparticle assemblies. We demonstrate that Chains Grafted at low densities follow Gaussian statistics at any dispersion states. These results suggest that Grafted Chains are not distorted but remain Gaussian when particles are aggregated into strings. Small-angle x-ray and neutron scattering results show that matrix Chains do not influence the formation of strings, but have a significant impact on the size and internal structure of aggregated particles. We conclude that spherical aggregates of nanoparticles with low polymer graft densities are akin to interpenetrating networks in which free matrix Chains bridge the fractals of particles and control the cluster density.
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accelerated brush growth on nanoparticle surfaces by reversible addition fragmentation Chain transfer polymerization
Journal of Polymer Science Part A, 2014Co-Authors: Yang Jiao, Pinar AkcoraAbstract:It is now well established that controlling the Grafted Chain lengths and densities on nanoparticle surfaces determines the effective interactions between particles, and their assembly. Here, we present unusual kinetic results for achieving Grafted Chain lengths longer than the free Chains using reversible addition-fragmentation Chain transfer (RAFT) polymerization and discuss the limitations to obtaining polymer grafting density higher than ∼0.06 Chains/nm2. We observe that surface initiated polymerization grows faster than the free Chains in solution with high RAFT agent coverage (1.95 agents/nm2) on nanoparticles. The time-dependence of graft density suggests that activation of the anchored Chain transfer agent (CTA) is limited by the diffusion of macro-radicals within growing grafts. Thus, radical transfer and exchange reactions become inefficient between grafts and free polymer, and convert the surface-initiated RAFT mechanism to a free radical polymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1700–1705
Yang Jiao - One of the best experts on this subject based on the ideXlab platform.
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understanding the role of Grafted polystyrene Chain conformation in assembly of magnetic nanoparticles
Physical Review E, 2014Co-Authors: Yang Jiao, Pinar AkcoraAbstract:Polystyrene-Grafted iron oxide nanoparticles have been shown to phase separate into ordered morphologies of strings, well-dispersed particles, and spherical aggregates at low graft densities in polymer matrices. In this work, small-angle neutron scattering experiments are performed to reveal the role of Grafted Chain conformation on nanoparticle assemblies. We demonstrate that Chains Grafted at low densities follow Gaussian statistics at any dispersion states. These results suggest that Grafted Chains are not distorted but remain Gaussian when particles are aggregated into strings. Small-angle x-ray and neutron scattering results show that matrix Chains do not influence the formation of strings, but have a significant impact on the size and internal structure of aggregated particles. We conclude that spherical aggregates of nanoparticles with low polymer graft densities are akin to interpenetrating networks in which free matrix Chains bridge the fractals of particles and control the cluster density.
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accelerated brush growth on nanoparticle surfaces by reversible addition fragmentation Chain transfer polymerization
Journal of Polymer Science Part A, 2014Co-Authors: Yang Jiao, Pinar AkcoraAbstract:It is now well established that controlling the Grafted Chain lengths and densities on nanoparticle surfaces determines the effective interactions between particles, and their assembly. Here, we present unusual kinetic results for achieving Grafted Chain lengths longer than the free Chains using reversible addition-fragmentation Chain transfer (RAFT) polymerization and discuss the limitations to obtaining polymer grafting density higher than ∼0.06 Chains/nm2. We observe that surface initiated polymerization grows faster than the free Chains in solution with high RAFT agent coverage (1.95 agents/nm2) on nanoparticles. The time-dependence of graft density suggests that activation of the anchored Chain transfer agent (CTA) is limited by the diffusion of macro-radicals within growing grafts. Thus, radical transfer and exchange reactions become inefficient between grafts and free polymer, and convert the surface-initiated RAFT mechanism to a free radical polymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1700–1705
